The invention relates to a method for the contact-free testing of an object, particularly microcircuits with a particle beam probe of a type well known in the prior art as described hereafter.
Structures which are becoming increasingly more detailed and small in printed circuit boards make it imperative to develop alternative test methods for the electric testing of microcircuits. For the electric continuity testing of microcircuits with mechanical needle adapters, given a reference grid scale of a printed circuit board of approximately 200 .mu.m or less, the limit is reached for the use of such mechanical needle adapters.
Alternative test methods with the aid of electron probes are known from the state of the art. For example, such a test method for the testing of microcircuits with an electron probe is known in which the resistance measurement of a printed conductor proceeds such that, with a first electron beam, a charge and hence a potential is impressed on one end of the printed conductor. If a conductive connection to the other end of this printed conductor exists then this other end of the printed conductor assumes the same potential, which can be checked with a second electron beam. This second electron beam is directed to the other end of the printed conductor. From this magnitude of the secondary electron signal then picked up from the other end of the printed conductor it can then be determined whether a conductive connection exists between the two ends of the printed conductor. This method exhibits the disadvantage that, in practice, it proves difficult to simultaneously produce two electron probes with varying energy and which are spatially closely adjacent to one another.
From Vac. Sci. Techol., Vol. 19, No. 4, November/December 1981, page 1016, incorporated herein by reference, an apparatus proposed by H. C. Pfeiffer et al with a total of 3 electron beam generators is known which permits a method for testing microcircuits with electron probes which can be practically carried out. In the case of this known method, with a first electron probe the specimen is charged and, with a second electron probe, the potential at one end of the printed conductor is altered in order to then determine with an electron probe the potential variation at the other end of the printed conductor. In the case of this known method, it turns out to be disadvantageous that the resistance of the printed conductor must be determined from a chronological potential variation and that, in the case of this known method, up to three electron beam generators are necessary.
The methods cited in the state of the art have the disadvantage that they do not operate in a load-free fashion, and that simultaneously the resistance of a printed conductor must be determined from the chronological variation of the charge state of the printed conductor.